Can evidence for spatial and/or temporal genetic heterogeneity of North Pacific minke whales be explained by different mixture fractions of the same two core stocks, or is it necessary to postulate an additional stock (s)?
Date of this Version
IWC Scientific Committee, 2011.
The analyses described here take advantage of the specificity of the two-stock mixing hypothesis for North Pacific common minke whales, which leads to some testable hypotheses based on standard population genetics theory. If the hypothesis is true (heterogeneity can be explained by different mixture fractions of the same two stocks, O and J, in different areas), loci with the largest allele frequency differences between J and O stock should show the largest departures from equilibrium when mixed samples are analyzed. Allele frequency differences were characterized by θ, an analogue of FST, and departures from equilibrium were indexed by FIS for single loci and by r2 (a measure of linkage disequilibrium) at pairs of loci. Samples from SA6 and SA9 were used to characterize putatively pure J and O stocks, respectively. Artificial mixtures of equal fractions of J and O individuals showed the expected strong correlations between θ and FIS (or θi θj and r2), but these were reduced somewhat when split-sample cross-validation was used, and when unequal mixtures were analyzed. Analysis of putatively mixed samples in general showed weaker correlations than were expected from mixtures of only J and O individuals. This novel type of analysis appears to hold some promise for informing conclusions about stock structure, but more evaluations are needed to determine how robust the results are.